Weird alpha bleeding
If you look closely, you can see that this is caused texture interpolation getting a little bit of the alpha surrounding the wood texture. So in other words, your wood texture is outlined with a line alpha less than a pixel wide which lets you see through to the objects and sky behind.



This is why you usually want to have a small margin around UVs so interpolation will have something outside with which to interpolate with besides alpha.

To fix this, you can try using the solutions below individually or in combination.


Scale the wood UVs in a little so the UVs aren't right up against the alpha:


This is really a pretty generous margin for this situation. In this case it only needs to be scaled in about half a pixel, but a little extra can't hurt.

Not completely ideal, as you lose part of the texture (though it's unlikely anyone would notice).
Disable interpolation. It won't completely get rid of the problem, as the texture is still filtered a bit when it's distorted by perspective etc, but it will be so small that it's only visible when viewed really close up. This way you can also save some memory by using the 512x512 texture, as it will no longer be blurred by interpolation if it's disabled.